1. Field of the Invention
The present invention relates to an apparatus and method of initializing a phase-change optical disk capable of repeatedly recording information, and more particularly, to an apparatus and method of initializing an optical disk which uses a UV lamp in order to crystallize a phase-change recording layer.
2. Discussion of Related Art
In general, in manufacturing an optical disk using a phase-change medium, initial crystallization means to make the phase-change medium into a zero-base. The optical disk can be recorded by instantly melting and rapidly quenching the disk using a laser beam to form an amorphous mark.
FIG. 1 is a plan view of a conventional ultra-small optical/magnetic disk. As shown in FIG. 1, the conventional ultra-small optical disk 10 includes an information recording zone 12 formed on a polycarbonate substrate, a metal hub 14 for supporting a spindle motor, and a center hole 16. A disk rim 18 having a width of 0.5˜1.0 mm is formed at the outermost periphery of the optical disk 10. A process of writing or reading information on or from the ultra-small optical disk 10 will be described as follows.
FIGS. 2A and 2B illustrate a structure of an optical disk having a phase-change medium as a recording layer, taken along a direction of a head of the optical disk. FIG. 2A is when the recording/reproducing head is opposite to the recording layer, and FIG. 2B is when the recording/reproducing head is in the same side as the recording layer. In the two cases, a laser beam 40 passes through a polycarbonate layer 20 and a first dielectric layer 22 to record a predetermined pattern on the recording layer 24 or read the recorded pattern. Then, the laser beam 40 passes through a second dielectric layer 26, but cannot pass through a reflective layer 28. A passivation layer 30 is formed on the reflective layer 28.
The most important thing in initializing the phase-change optical disk is that it may be possible to generate degradation of the polycarbonate substrate very sensitive to heat during an initial crystallization process, and an initialization time should be shorter in order to increase productivity of the disk. The polycarbonate substrate is deformed at about 130° C. Therefore, it is impossible to use a constant temperature furnace in order to initialize the phase-change optical disk.
A conventional method of initializing a phase-change medium are disclosed in Korean Patent Laid-open Publication No. 2004-75705, published on Aug. 30, 2004, entitled “Method of initializing optical recording medium”, Korean Patent Laid-open Publication No. 2001-6496, published on Jan. 26, 2001, entitled “Method of manufacturing optical information recording medium and optical information recording medium manufactured using the same”, U.S. Pat. No. 6,335,069, issued on Jan. 1, 2002, entitled “Phase-changeable optical recording medium, method of manufacturing the same, and method of recording information on the same”, and so on. A conventional method of initializing a phase-change medium will be described with reference to the conventional arts disclosed in the Patents.
First, a typical method of initializing a phase-change medium in the conventional arts uses a high-output laser having a long wavelength of about 800 nm, and irradiates the laser on an area of several μm2 using a head including a low aperture lens to repeatedly scan a plurality of tracks at a time while rotating a disk at a high speed, thereby uniformly initializing the entire medium. The track includes a land and a groove. In this case, an initialization apparatus is very expensive, and in the case of initializing a 5-inch disk, it takes an average time of about 1 minute.
Next, among technologies on initialization of the phase-change medium, there are two methods using a method of manufacturing a medium not requiring initialization. One method is to form a crystallization promotion layer before deposition of the recording layer. The crystallization promotion layer, referred to as “an additional layer”, is made of a material having a melting point lower than that of the recording layer and a small difference between lattice constants of a crystalline phase of the recording layer and the additional layer to be easily formed as the crystalline phase on deposition of the recording layer. The crystallization promotion layer is formed of Sb, or SbTe-based alloy, Bi, or an alloy containing Bi. While the method does not requires an initialization apparatus and an initialization time, it may be possible to generate degradation of disk characteristics due to inter-diffusion between a phase-change promotion layer and the recording layer by repeating recording and reproducing operations. Another method is to increase a deposition temperature higher than the atmospheric temperature using a method of crystallizing the recording layer simultaneously with the deposition, without using the phase-change promotion layer. The recording layer has a crystallization temperature of about 150° C. and the method uses kinetic energy of particles on deposition at a temperature lower than the crystallization temperature, thereby enabling the crystallization. However, the method has a problem that the substrate may be deformed due to deterioration of the substrate when polycarbonate is used as the optical disk substrate.
Other initialization methods are to use a transparent laser having a wavelength not more than 400 nm in order to improve irregular initialization during an initialization process, and so on.